Optical cables include optical waveguides such as optical fibers that transmit optical signals such as voice, video, and/or data information. One type of fiber optic cable is a breakout fiber optical cable. A breakout fiber optic cable generally includes several protected structures that are capable of being broken-out from an assembly or cable and run to desired locations for optical connection.
U.S. Pat. No. 5,857,051 is an example of a breakout fiber optic cable that discloses a plurality of optical fiber ribbon structures in a tube. As depicted in FIG. 1, an optical fiber ribbon structure 10 requires a fiber optic ribbon 12 and a plurality of strength members 16 surrounded by a relatively loose sheath 18. Strength members 16 are aramid fibers that are used to protect a plurality of optical fibers 12a of fiber optic ribbon 12 from breakage due to tensile forces applied to the optical fiber ribbon structure 10. The fiber optic cable can include flame-retardant materials for riser or plenum applications; however, this cable has disadvantages.
For example, since sheath 18 is relatively loosely disposed around the optical fiber ribbon 12, ribbon 12 can rotate relative to sheath 18 as depicted in FIG. 1a. Stated another way, when the ribbon structures are stranded within the tube, portions of optical fiber ribbon 12 can twist and contact the inner wall of sheath 18 causing local stress points. These local stress points can cause undesired optical attenuation in the optical fibers adjacent to the local stress point and may even render the optical fibers inoperable. Additionally, when subject to temperature variations, sheath 18 can shrink which can cause stresses and/or strains on optical fiber ribbon 12. For instance, the shrinking sheath 18 can cause a compressive force that undulates or buckles optical fiber ribbon 12 along its length, thereby causing undesired optical attenuation. Additionally, optical fiber ribbon structure 10 has a relatively large cross-sectional area that generally decreases the number of optical fibers that can fit within the tube.